Islamabad, Pakistan (CNN) -- The death toll from the strong earthquake that struck southwestern Pakistan this week has risen to 356 as rescue workers struggle to reach victims, authorities said Thursday.
Further complicating relief efforts, two rockets were fired at -- and missed -- a military helicopter on its way to the quake zone.
The number of people injured has climbed to 619, said Jan Muhammad Buledi, a spokesman for the government of Balochistan, the province where the quake hit. Authorities estimate that 21,000 houses have been destroyed.
The 7.7-magnitude earthquake took place Tuesday in a remote, sparsely populated area of Balochistan. Rescue efforts are under way in the heavily hit districts of Awaran and Kech.
Images from the scene have shown buildings reduced to rubble. More people are feared to be trapped under the wreckage, authorities say, suggesting the death toll could rise.
The remoteness of the affected area and damaged communications networks are hindering the rescue operation.
Officials say some areas remain inaccessible, preventing them from getting a full picture of the scale of the damage.
Meanwhile, thousands of survivors in need of assistance after the quake are having to cope with high temperatures, a lack of drinking water and little in the way of shelter.
October is the hottest month in Balochistan and the region is in a perpetual state of drought, said Muhammad Hanif, the director of the National Weather Forecasting Center. Temperatures in Awaran and Kech have reached 37 degrees Celsius (99 degrees Fahrenheit).
The Pakistani military has deployed more than 1,000 troops to help with rescue and relief efforts
The troops are entering a difficult region. Militants fighting for a separate state in Balochistan operate out of part of Awaran district, which has been the site of bombings.
The potential threat was underlined Thursday when two rockets were fired at an army helicopter ferrying the chairman of the National Disaster Management Authority to the earthquake zone, a military official said.
The rockets missed the helicopter as it flew over the narrow Mashki Valley on its way to Awaran, said Brig. Muhammad Abdur Raheem, an army spokesman in Balochistan.
The helicopter was carrying Maj. Gen. Muhammad Saeed Aleem, the National Disaster Management Authority chairman, as well as staff officers and two members of the local news media, Raheem said. All those who were aboard are safe, he added.
There was no immediate claim of responsibility for the failed attack.
Pakistani officials have said the quake was powerful enough to cause the appearance of a small mud island a few kilometers off the country's coast in the Arabian Sea. But some overseas scientists have questioned whether the island was the direct result of the earthquake.
CNN's Saima Mohsin in Islamabad contributed to this report.